The Meihomian glands of the sow are small ; representing merely a short cyst subdivided into several loculi. The glands of the eye lashes in the same animal are, on the contrary, large. The Meibomian glands of the sheep, dog, and fox, are long very thick-walled bodies, in the middle of which there is a wide canal. Ranking next in complexity of structure are the human Meibomian glands. Those of the horse, ox, goat, and cat; Zeiss found still more complex, consisting of lobes, lobules, and granules.* The secretion of the Meibomian glands is a mild, yellowish, unctuous substance, of the consistence of lard. Occasionally the external orifice of one or more of the Meibomian ducts becomes covered by a thin film, apparently of epidermis. This prevents the escape of the secretion, which accumulating raises up the film into a small elevation, like a phlyctenula. This does not actually cause pain, but gives rise to uneasiness in the part when the eyelids are moved : the film is easily broken, and the accumulated secretion removed on the point of a pin.
Hordeolum, or stye, according to some, is abscess of the Meibomian glands ; according to others, a small boil implicating the cellular tissue at the margin of the eyelid. Zeisst sus pects it has its seat in the capsule and glands of the roots of the eyelashes. Abscess of the Meibomian glands does occur, and gives rise to a tumour on the edge of the eyelid like a stye, but the nature of the case is seen on everting the eyelid. There can be no doubt that the roots of the eyelashes are involved in the disease, because the hairs at the part affect ed generally fall out at the end. Dr. Zeiss proposes to anticipate this result by plucking them out at once, and he says that by this pro cedure the progress of the complaint is arrested, a thing, certainly, occasionally very desirable. In a small inflammatory tumour at the root of a hair on the cheek, I have obtained such a result from plucking out the hair.
II. The conjunctiva, semilunar fold, and lacrymal caruncle.
The conjunctiva in general.—Tunica con junctiva seu adnata. Fr. La Conjonctive. Ital. La Congiuntiva. Germ. Die Bindhaut. The conjunctiva is that membrane which lines the posterior surface of the eyelids, and covers the front of the eyeball to the extent of about a third of its whole periphery. This disposition has given rise to the distinction of a palpebral and ocular conjunctiva. Towards the margin of the orbit, all round the circumference of the eyeball, a cul-de-sac is formed by the reflection and continuation with each other of these two portions of the membrane. It is by this conti
nuity that the eyelids and eyeball are held in connexion, hence the name conjunctiva, and that the orbit is closed in and cut off from all communication with the space between the eyeball and eyelids.
The space between the eyelids and eyeball we shall distinguish by the name of oculo-palpebral space of the conjunctiva, a name, the necessity for which appears from this, that in common language, when it is said a foreign body has got into the eye, it is only meant that it has got into the oculo-palpebral space of the con junctiva. The propriety of the name moreover will become more evident when the space in Serpents and Geckoes comes under considera tion, for in them it is a closed cavity, (in ser pents already designated by Jules Cloquet* oculo-palpebral sac of the conjunctiva,) re ceiving the lacrymal secretion and communi cating with the exterior only by the connexion it has with the nose through the nasal duct.
What are called the superior and inferior palpebral sinuses of the conjunctiva are those parts of the oculo-palpebral space under the upper and lower eyelids respectively, where the ocular and palpebral portions of the con junctiva are reflected and continued into each other, forming a cul-de-sac. The conjunctiva is here loosely attached to the subjacent cellular and adipose tissue, &c. of the orbit, and forms folds constantly varying with the motions of the eyeball and eyelids. The superior palpebral sinus of the conjunctiva is deeper than the lower, the reflection of the conjunctiva from the eyelids upon the eyeball being when the eyelids are passively closed : above, at the distance of about seven-tenths of an inch from the margin of the upper eyelid, and below, at about three tenths of an inch from the margin of the lower. The cul-de-sac formed by the reflection of the conjunctiva does not lie very deep within the outer canthus, speaking in reference to it alone, though as near the edge of the orbit as above or below.
The looseness of the folds formed by the conjunctiva at the upper and lower palpebral sinuses and within the outer canthus, together with the peculiar nature of its disposition at the inner canthus, presently to be noticed, allows of the free motions of the eyeball in all direc tions. These folds may be readily seen on everting either eyelid, as also the continuity of the conjunctiva from the eyelid to the eyeball by requesting the person to look upwards, if it is the lower eyelid which is everted, downwards in the contrary case.